Sierra Monitor Corporation Carbon Monoxide Alarm TR 001 User Manual

Technical Reprint TR-001  
To minimize risks, a plant-wide gas monitoring system must meet the specific needs of  
the facility in terms of system inputs and outputs and data acquisition.  
Plant-Wide Gas Monitoring for Risk Control  
as monitoring has become an integral part of many environmental protection and safety programs. Because of  
Gincreased attention to risks posed by gas, systems that simply annunciate an alarm condition are no longer  
adequate. Gas monitoring programs now comprise employee training, data analysis, multiple alarm strategies,  
self-diagnostic system verification, and documentation. Data communication has also become a fundamental  
component of system design and operation as well. And finally, environmental factors help guide the program  
selection process.  
GAS MONITORING RATIONALE  
Gas Monitoring is an integral part of environmental protection and safety programs. There are three major  
categories of hazardous gases. Combustible gases pose a risk to personnel and facilities through fire or explosion..  
Oxygen displacing gases deplete workers' oxygen supply in confined spaces. Toxic gases create both immediate  
and long term risks to personnel. Toxic gases are those OSHA and other organizations have defined as hazardous to  
human health. They are typically monitored both below and above the threshold limit value (TLV). TLV is an  
8-hour time weighted average concentration that is the highest value acceptable as a safe working environment.  
System design requirements such as the number of sensors required, sensor placement, and system alarm levels will  
vary according to the type of gas.  
A properly designed gas risk management program can reduce risk. A successful program needs to first, identify the  
hazards at the facility, then assess the risk of a hazardous event to the plant, personnel, the community and the  
environment. Next, the program needs to comply with insurance, legal and regulatory requirements. Also, liabilities  
and financial risks need to be evaluated. Finally, the program must incorporate company safety philosophies.  
Through such a program you can reduce the risks associated with hazardous gas leaks at your facility. Sierra  
Monitor offers products that provide critical data to prompt corrective action before a minor leak becomes a major  
event. Information can be retrieved from the equipment display, printed locally or recorded by a computer. This  
information aids in evaluating potential hazards in relation to operating practices.  
Hazard Identification &  
Assessm ent  
Risk to  
Environm ent  
Laws &  
Com pany  
Regulations  
Philosophy  
Risk to  
Personnel  
Risk to  
Facility  
Insurance  
Requirem ents  
Financial  
Risks  
Liability  
Control System  
Capability/Cost  
Tradeoffs  
Decision,  
Control Strategy,  
System Selection  
Risk Reduction  
Sierra Monitor Corp. 1991 Tarob Ct., Milpitas, California 95035 USA 408-262-6611, 800-727-4377 FAX: 408-262-9042  
 
Technical Reprint TR-001  
PLANT-WIDE MONITORING  
Plant-wide gas monitoring offers many benefits, among them:  
Centralized monitoring of all gas measurements  
Monitoring the status of control elements  
Establishing a “command center” to respond to alarm events  
Remote access to all system data  
Centralized reporting  
In a plant that has been instrumented over a period of years, the gas detection system is likely to be an autonomous  
installation. The controller might be in the field close to the sensors or in a control room. Both approaches have  
limitations. Controllers in the field do not transfer gas concentration information to the control room. Alarm data  
are limited to local annunciation of an alarm event, or long wiring runs are required in order to report sensor-by-  
sensor alarm status to a central control room. Alarms are therefore usually limited to relays activated by groups of  
sensors and/or field controllers in a given area.  
Controllers located in the control room usually require extensive wiring to the sensors and alarm activity is often  
minimized to reduce wiring cost. Furthermore, when the controller is in the central control room, there are no  
concentration data available in the field for plant personnel to make on-the-spot decisions; only an alarm light or  
horn is activated.  
Systems designed for plant-wide monitoring avoid these deficiencies. They:  
Accept sensors for multiple gases  
Accept sensors from various manufactures  
Accept other environmental and process sensor measurements  
Provide local display of gas concentration  
Permit auto-adjusting calibration  
Accept feedback signals from final control elements  
Provide independent battery backup  
Allow low-cost communications link to the control room  
Provide relays for local alarm action  
Implement user-defined alarm strategy  
Provide centralized monitoring of sensor status as shown on the plant log plan and at each operation /  
facility with bar graphics, configuration screens, and real-time trends  
Provide centralized data logging  
Provide alarm acknowledgment from the control room  
Allow access to control room computer from other sites in facility  
Operate independently even if communications with the control room are severed  
Provide for easy system reconfiguration via computer at the control room  
Distributed intelligence is central to system design philosophy. Because the field controllers can implement alarm  
logic and operate independently of the host computer, they do not interrupt or hamper field operation. A plant-wide  
monitoring system provides the user with clear, understandable data that make it possible quickly to analyze the  
situation and take appropriate action. A correctly designed plant-wide monitoring system offers the best features of  
local control, and centralized monitoring systemizes the entire monitoring process.  
CRITICAL SYSTEM COMPONENTS  
The components of the system are the sensors, the field controller, and the monitoring software. Sentry, from  
Sierra Monitor, is an example of a system that can implement plant-wide gas monitoring. The gas sensor modules  
can be multiplexed on a single cable back to the controller.  
To offer complete solutions at each site, field systems need full I/O capability. Sentry fulfills this requirement by  
accepting a variety of sensors or 4-20 mA transmitters. The Sentry controller is an intelligent device that can access  
the sensor modules for diagnostic data, non-intrusive calibration and gas concentration information.  
MODBUS communications interface enables Sentry and the IT Series sensors to easily interface with a PC-based  
Distributed Control System (DCS) providing a graphical display of hazardous gas conditions in the plant. PC-based  
Sierra Monitor Corp. 1991 Tarob Ct., Milpitas, California 95035 USA 408-262-6611, 800-727-4377 FAX: 408-262-9042  
Visit our Web Site at: http://www.sierramonitor.com  
 
Technical Reprint TR-001  
DCS software in conjunction with Sentry provides the operator enhanced data acquisition, alarming and alarm  
management, historical trending, distributed architecture, and integration into the plant's distributed control system.  
Sentry's MODBUS communication interface provides over 620 different parameters accessible by the PC-based  
DCS software, including:  
Gas concentration  
Alarm setpoints  
Sensor diagnostic messages  
Historical reset time/date  
Power up/down time/dale trouble alarm time/date  
Minimum/maximum values plus time/date  
High/low alarm latch/non-latched  
Auto calibration enabled  
Calibration status/coefficients  
Calibration concentrations  
Calibration due date  
Zone option enabled  
Operate mode  
With the MODBUS communications option for Sentry and the graphic based man-machine software program a  
variety of graphic screens can be developed. These screens make it easy for the operator to efficiently monitor haz-  
ardous gas risks in any plant. Typically the system will include a main screen providing an overall view of the plant.  
This screen is linked to individual zone displays, historical and real-time trend charts, bar charts indicating gas  
concentration and alarm levels, and more.  
SUMMARY  
The key to any plant-wide monitoring system is the flexibility to configure system inputs/outputs and data  
acquisition to meet the specific needs of the plant. By monitoring sensors throughout the plant, better visibility of  
the ambient environment can be realized and more informed decisions can be managed in the event of gas exposure.  
A plant-wide monitoring system using distributed intelligence coupled with advanced PC based software offers an  
improved approach to limit in plant risks. The benefits to employee safety and environmental responsibility are  
self-evident, as are the economic rewards of reducing the chance of loss from interruptions in operation and from  
litigation. Risk minimization, including plant-wide gas monitoring, makes good business and social sense.  
Sierra Monitor Corp. 1991 Tarob Ct., Milpitas, California 95035 USA 408-262-6611, 800-727-4377 FAX: 408-262-9042  
Visit our Web Site at: http://www.sierramonitor.com  
 

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